Pyroengineering. A big word for what early modern humans learned to do at least 72,000 years ago, according to researchers.

A team of archaeologists says that ancient humans harnessed the power of fire to transform stone raw material into an improved form for tool making. It’s next to impossible to fashion sharp stone blades from a stone called silcrete as it naturally occurs. But if silcrete is heat treated, it can then be worked into advanced tools.

This complex technology is another example of that behavioral modernity we are calling the Human Spark – and it’s occurring on the southern tip of Africa tens of thousands of years earlier than the Human Spark is evident in Europe.

When the Human Spark team filmed with Arizona State University’s Curtis Marean, he told Alan Alda about his group’s discovery at Pinnacle Point in South Africa. Watch this video to hear how the scientists figured out the secret of the silcrete.